The scope of this project is to elucidate pathogenic mechanisms involved in infections of mink with Aleutian mink disease parvovirus (ADV). In the past year, we developed a method for in situ hybridization using nonradioactive probes. Nonradioactive probes provide a clearer picture of cellular morphology than radioactive probes, although they are noticeably less sensitive. Using both probe types, we have attempted to identify more closely the target cells for ADV replication in adult mink. Our previous work indicates the target cells are found in lymph nodes and have the distribution of follicular dendritic cells and macrophages. Using probes specific for virion DNA sequestration, we localized virion sequences in both macrophages and follicular dendritic cells. However, using conditions specific ADV mRNA, ADV replication could be conclusively localized only to macrophages. Attempts to isolate macrophages and follicular dendritic cells from infected mink lymph nodes yielded low numbers of cells with poor viability. Furthermore, extremely low numbers of ADV infected cells could be found in these populations ass assessed by in situ hybridization and the type of cell could not be defined. Cells from the peritoneal cavity of ADV infected mink were also studies. Cells containing ADV nucleic acid were readily identified. The number of cells containing virion DNA was about 10 times that of cells with ADV mRNA. Some of these cells were phagocytic, supporting the notion that macrophages are target cells for ADV. Finally, adherent resident peritoneal cells from normal mink were infected in vitro with ADV and a small number of these cells replicated ADV as assessed by the production of ADV antigens. In other work, we began to study the transcription program of ADV in vivo. Northern blot analysis of mRNA from the lungs of infected mink kits suggested that ADV transcription in this tissue is similar to that observed in permissive in vitro infections. mRNA from the lymph nodes and peritoneal exudate cells of infected adult mink also had detectable ADV mRNA, but the amount was low. Nevertheless, all ADV mRNA species appeared to be present.